Re: [RFC 1/2] PM / Domains: Power on domain early during system resume

From: Andrzej Hajda <a.hajda@samsung.com>
To: Krzysztof Kozlowski <k.kozlowski@samsung.com>,
	Kevin Hilman <khilman@kernel.org>
Cc: Len Brown <len.brown@intel.com>,
	Kukjin Kim <kgene.kim@samsung.com>,
	linux-pm@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	Seung-Woo Kim <sw0312.kim@samsung.com>,
	Kyungmin Park <kyungmin.park@samsung.com>,
	linux-samsung-soc@vger.kernel.org, Pavel Machek <pavel@ucw.cz>,
	linux-arm-kernel@lists.infradead.org,
	Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [RFC 1/2] PM / Domains: Power on domain early during system resume
Date: Thu, 30 Oct 2014 12:01:35 +0100	[thread overview]
Message-ID: <54521A8F.5070808@samsung.com> (raw)
In-Reply-To: <1414654594.5114.8.camel@AMDC1943>

On 10/30/2014 08:36 AM, Krzysztof Kozlowski wrote:
> On śro, 2014-10-29 at 10:46 -0700, Kevin Hilman wrote:
>> Krzysztof Kozlowski <k.kozlowski@samsung.com> writes:
>>
>>> When resuming the system the power domain has to be powered on early so
>>> any runtime PM aware devices could resume.
>>>
>>> This fixes following scenario reproduced on Exynos DRM:
>>> 1. Power domain is off before suspending the system.
>>> 2. System is suspended to RAM.
>>> 3. Resuming starts. The Exynos DRM driver resume callback is called.
>>> 4. The Exynos DRM driver calls drm_helper_resume_force_mode which turns
>>>    the screen on by calling exynos_dsi_dpms with DRM_MODE_DPMS_ON.
>> Dumb Q: if the device (and power domain) were off before (and during)
>> suspend, why are they being resumed?
>>
>> Shouldn't the resume path restore things to the same state they were
>> before suspend?
> One could expect that... but the Exynos DRM driver behaves differently
> (and some other drivers also). In resume method it calls
> drm_helper_resume_force_mode() which forces restoring mode setting
> configuration. Apparently setting a mode needs DPMS on:
> static void exynos_drm_crtc_commit(struct drm_crtc *crtc)
> {
> 	...
> 	exynos_drm_crtc_dpms(crtc, DRM_MODE_DPMS_ON);
> 	...
>
> The previous DPMS status (status during suspend) is completely ignored
> here.

Suspend callback switches off all connectors (thus all other devs in
their pipeline) by calling dpms_off,
in restore callback all devs are restored to their previous state by
calling appropriate dpms.
So I guess drm_helper_resume_force_mode() call at the end of resume is
incorrect.
On the other side it is present in many other drivers, so I am also
little bit confused.

Regards
Andrzej

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